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TI-2021-19598 Aliases CVE-2021-43791

Ineffective expiration validation for invitation links in Zulip

Priority LOW 30CWE-613Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-613.

Summary

Zulip is an open source group chat application that combines real-time chat with threaded conversations. In affected versions expiration dates on the confirmation objects associated with email invitations were not enforced properly in the new account registration flow. A confirmation link takes a user to the check_prereg_key_and_redirect endpoint, before getting redirected to POST to /accounts/register/. The problem was that validation was happening in the check_prereg_key_and_redirect part and not in /accounts/register/ - meaning that one could submit an expired confirmation key and be able to register. The issue is fixed in Zulip 4.8. There are no known workarounds and users are advised to upgrade as soon as possible.

Why it matters now

EPSS 0.00663 51st percentileScored 2026-11-07
Fix Fixed zulip (zulip): 4.8

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
zulipzulipbefore 4.84.8Patch availableCNA
  • zulip Vendorzulip Affected before 4.8 Fixed in 4.8 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:zulip:zulip:*:*:*:*:*:*:*:*before 4.8Vulnerablezulip
  • cpe:2.3:a:zulip:zulip:*:*:*:*:*:*:*:* Versions before 4.8 Vulnerable ·zulip

Remediation

  • Fix · CNA zulip (zulip) Fixed in 4.8

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-43791
  2. 2026-10-06 EPSS moved to the 50th–90th percentile

References

Patch 1

Advisory 1

  • TI-2026-20810 Zulip: Anonymous File Access After Disabling Spectator Access CVSS 3.1MEDIUM 5.3
  • TI-2026-21062 Zulip: Path Traversal in Import CVSS 3.1MEDIUM 6.1
  • TI-2021-19605 RabbitMQ exposes ports with weak default secrets in Zulip Server CVSS 3.1CRITICAL 9.8
  • TI-2023-15953 Users who can send invitations can erroneously add users to streams during invitation in Zulip CVSS 3.1LOW 3.1
  • TI-2022-13210 Zulip Server insufficient authorization for changing bot roles CVSS 3.1HIGH 8.8
  • TI-2021-02864 Improper Access Control in zulip/zulip CVSS 3.1HIGH 8.8
See all 19 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences